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Buzzers and bells and alarms.

Buzzers and bells and alarms.

Introduction: (Initial Observation)


The electric bell is among the most common electrical equipment found in every house or office. It is used as a door bell, phone ring, fire alarm and can be found in many different shapes and sizes. An electric bell is a simple example of how we can convert electrical energy into mechanical energy and sound waves. The same mechanism used to vibrate a hammer in an electric bell, is used in many other industrial and household equipment.

Two well known examples are Electric Shavers Shearing machines. These two both work like a buzzer (Another name for an Electric Bell), but instead of a hammer, a blade will be vibrated. In this project you will make a bell or a buzzer to demonstrate the vibration motion produced using an electromagnet.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Adult supervision and help is required in this project.

Information Gathering:

Find out about the electromagnet and how it can be used to construct various electrical devices. Read books, magazines or ask professionals who might know in order to learn about the structure of a buzzer. Keep track of where you got your information from.

Following are samples of information that you may find:


The basis for any buzzer or bell is the electromagnet. Andre Ampere invented the electromagnet in 1825. An electromagnet is essentially an insulated wire wrapped around an iron core that is magnetized only when electrical current flows through the wire. This is something that can be easily made at home using several components.

Make a simple Electromagnet

To construct an electromagnet you will need insulated wire, an iron core (Hint: A nail is usually made of iron), and a battery (a 6 volt heavy duty battery works the best). The battery is your source of power and what it produces are electrons. Each battery has a positive end and a negative end. To construct an electromagnet you can simply wrap an insulated wire around an iron nail (about 100 turn) and connect the two ends of wire to the two ends of a battery. Just make sure that you remove the insulation from the ends of the wire.

The electric bell is a type of bell operated by an electric current. There are two types of electric bells. One type rings continuously when the switch that controls it is on. This type of bell is commonly used in schools and factories. The other kind, the door chime, rings only once or twice when the switch is turned on–that is, when the doorbell button is pushed.

The parts of a continuously ringing bell include the switch; an electromagnet, a device that acts as a magnet when a current runs through it; and an armature, a movable metal part. A clapper is attached to the end of the armature. Also attached to the armature is a spring that rests against a screw. Wiring runs from the source of electric current to the switch and from the switch to the electromagnet. Another wire runs from the screw back to the source of the electrical current. Together, the parts of the bell form an electrical circuit.

When the switch is turned on, the current flows through the electromagnet, and the electromagnet attracts the armature. The movement of the armature causes the clapper to strike the bell and the spring to move off the screw. When the spring moves off the screw, the circuit is broken and the current stops flowing. Then, the armature falls away from the electromagnet. When the armature returns to its original position, the spring comes in contact with the screw again and reestablishes the flow of electric current. The process repeats and the electric bell keeps ringing as long as the operating switch is on.

A door chime does not have the spring and screw. Thus, the armature and clapper move only once each time the control switch is operated, and the bell sounds only once. If a second bell is set up for the clapper to strike when it falls away from the first bell, two sounds can be produced for each switch operation.

This drawing shows how an electric bell works:

1st step    The switch is closed
2nd step   A current flows
3rd step    The iron bar is magnetized
4th step    The iron armature is attracted
5th step    The armature moves to the left
6th step    The hammer hits the gong
7th step    The circuit is now broken
8th step    The armature moves back
9th step    The circuit is again complete

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to find out how an electric bell works and what factors affect its function.

An electromagnet is the main part of any door bell. A weak electromagnet will not have enough force to pull the armature; Thus, the main question for this project is:

How does the size of a coil affect the strength of an electromagnet?

Alternatively you could select any of the following questions for your project.

How can we make the electromagnet stronger?


How does the core of the coil affect the strength of the electromagnet?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

We are trying to find out how does the number of loops in the electromagnet’s coil, affect the strength of the electromagnet; Therefore, the variables are as follows:

Independent variable (manipulated variable) is the number of loops.

Dependent variable is the strength of the electromagnet.

Constants are the voltage, wire thickness, wire type, core size and type.

Controlled variables are environmental conditions such as temperature; thus perform all the experiments in the same environmental conditions.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

From your question you can devise a sample hypothesis. For example:

Wrapping the wire around the iron core makes the magnetic field stronger.

Another example could be:

The size of the coil is directly related to the magnets strength.

The hypothesis does not have to be correct, we will later revisit this statement when we obtain results from our observations.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”


Introduction: In this experiment you will test the effect of coil size (number of loops of wire) on the strength of an electromagnet. Essentially, you are going to observe the change on the magnets strength as caused by the size of the coil. To test the magnets strength you can use a magnetometer or simply do it by observation. Since we do not need to measure the actual strength of the magnet but just the change as we manipulate the dependent variable, we can use the observation method. To do this, you will need some small screws or nails that are the same size. Compare the strength of your electromagnets by seeing how many nails it can attract.


Get 10 identical iron nails or rods (about 2 inches long) as the cores for electromagnets that you are going to make. Number them from 1 to 10 by attaching small stickers to the heads of the nails.

Leave about 1 foot wire and then start to wrap 25 turns of insulated wire around the nail number 1. Leave another foot of wire and then cut from the spool. In this way you will have 25 turns of wire on the nail and one foot of free wire on each end. Remove the insulation from the ends of wire so you can see the bare wire. Wrap some masking tape over the coil to secure the coil wire.

Repeat the above procedure with nails number 2 to 10 in a way that each nail will have 25 turns of wire more than the previous one. In this way you will have 10 coils of wire with 25, 50, 75, 100, 125, 150, 175, 200, 225, 250 loops of wire.

Connect each wire coil (electromagnet) to a 1.5 volt battery and hold it above a bunch of small nails. Lift it and move it aside. Disconnect the battery so the nails will fall. Count the number of nails. Repeat this 3 times and take the average of the number of nails. Record the average in your results table.

Your results table may look like this:


Independent Variable (number of coils) Dependent Variable Change
(number of nails lifted)
25 coils
50 coils
75 coils
100 coils
125 coils
150 coils
175 coils
200 coils
225 coils
250 coils


Make a graph:

Make a bar graph with 10 vertical bars. Each bar will represent one coil size starting from 25 up to 250. Write the coil size below each bar. The height of each bar must show the number of nails that one specific coil can lift.

If you need to draw other types of graph, please see the graph information in the “How to Start” section.

Note1: The above procedure is only an example; don’t be afraid to do something different. For example, you can increase the coils by a bigger amount. Testing the independent variable using a bigger change in the dependent variable (in multiples of 10 for example) will give you clearer results.

Note 2: You can use a number of different independent variables. The number of coils is only an example. If you want you can try using different sources of power, such as batteries with different volts, different size wire (thicker gauge wire allows more current to flow through it faster), or another metal core. All of these will have different effects on the strength of the electromagnet. The important thing to remember is to only change one independent variable at a time so that we can observe which variable actually caused the change.

Why we study Electromagnets?

The experiment you have just conducted is that of an electromagnet. This electromagnet is used in buzzers, bells, and alarms. It is important to realize that the electromagnet is precisely what makes these devices function. It does so by causing interaction between that contact arm and a metal contact. When you push the button to sound the buzzer commonly found in a doorbell, you are causing the electromagnet to attract the contact arm. By attracting the contact arm, the circuit is broken and the electromagnet shuts off, allowing the contact arm to fall back down onto the metal contact. This continuous motion between the contact arm and the metal contact causes the buzzing sound that you hear. By holding the doorbell button you are actually causing the electromagnet to break the circuit continuously until you let go. A bell works the same way as a buzzer. The only difference is that the contact arm is connected to a clapper (hammer) that continuously hits the bell as the electromagnet attracts the contact arm away from the metal contact. You now have a real life application of the electromagnet.

Make an Electric Bell:

Basic design of an electric bell consists of an iron bar (armature) that will be attracted by an electromagnet. Therefore, I start my project by building an electromagnet and mounting it on a piece of wood. Then I will mount an armature about 3 millimeters above the electromagnet, secured from one side by a hinge or spring tempered sheet of iron. If my armature is very flexible, I can just mount it using a screw or nail.

Use a piece of wood about 5 inches wide and about 7 inches long. It should be tick enough so you can make a hole on that and secure other components using screws and nails.

To build an electromagnet you can use any screw or nail. It can be about 2 inches tall and and quarter inch diameter. In this experiment we will mount the electromagnet vertical to the base board.

Make a hole and secure the nail or screw in the hole. At least one inch of that should be out to form the electromagnet.

Wrap some paper or tape around the coil as an insulator.

Get some magnet wire and turn it around the nail or screw to form the coil of your electromagnet. Magnet wire is regular copper wire coated with some resins as an insulator. They call it magnet wire because it is used to build electromagnets.

The thickness of the magnet wire must be less than 1/32 inches or 0.03 inches. Otherwise the coil gets hot and lots of energy will be wasted as heat. Also the coil must have more than 100 loops. More loops creates a stronger electromagnet.

Use sand paper to remove the insulation of magnet wire at both ends.

You can also use small screws to secure the ends of magnet wire.

Connect the electromagnet to a 6 volt battery. Use a screw driver or nail to see how strong it is.

I found a Popsicle stick and decided to use it as an armature. Since electromagnet can not attract wood, I warped a piece of thin iron sheet around that. I got may metal sheet from a chocolate box and I could cut it using scissor

After securing the Popsicle stick with two screws, I connected one end of the coil wire to the negative pole of battery and the other end to the metal sheet on the Popsicle stick. Then I used another wire and connected one end of that to the positive pole of the battery and used the free end to touch the metal piece on the armature. As soon as this last wire touched the metal sheet, the buzzer started to work.

The wire in my hand and the metal on the armature together act like a switch that connects and disconnects. I call it a contact switch. In this picture I used another piece of metal sheet to hold the wire above the armature.

Note: First I tried using the last metal sheet to be the contact switch, but the magnet attracted that and the switch never opened. That’s why I finally used another copper wire to be the contact switch.

You will need to repeat such experiments with different number of loops on the coil and different batteries (1.5 volts, 3 volts, 6 volts) and compare and report the results

Another Design

In this design blue dots are nails.
A is an electromagnet made from a bolt and copper coil of more than 100 loops.
B is the armature. It is galvanized or black iron. One end is rolled so we can use a nail. It will be mounted in a way that it stays about ¼ inch away from the electromagnet.
C is contact metal made from copper. It should be touching the armature in a way that it gets disconnected when armature is about half way down. C will be secured on the board using a small screw.
D is a spring to keep armature up. We wouldn’t need it if our armature was spring tempered metal and we could secure it from one end.
E is the gong. Anything that can make sound.

As you will see in the following pictures I have installed the contact metal C almost at the hammer part of the armature. I did that because my board was small and did not have enough room above the armature to mount the contact metal.

In this new design we use a bolt and a nut to build the electromagnet.

Wrap the coil with some tape and mount it on the board using a copper strap.

The armature is a flat sheet of galvanized iron, less than one inch wide and about 8 inches long. I rolled one end so I can use a nail to mount it on the board. I also folded or bended the other end to act like a hammer. The contact switch is a small piece from a copper sheet.

Since this armature also was not a spring, I added a spring to pull it away from the electromagnet. To make sure that the armature will stay close to the electromagnet I also inserted another nail to make sure the armature does not get pulled away and get very far from the electromagnet.

An empty can worked as a gong

As you see, buzzers and bells can be constructed in many different ways; however the concepts and methods are the same.

Following are some additional images of buzzers with similar designs.

Materials and Equipment:

List of material used in the experiment section:

  1. 100 feet magnet wire (insulated wire) gauge 24, 26 or 28
  2. 10 Short, thick iron nails or rods
  3. Bunch of small nails or similar same size iron pieces
  4. One or more 1.5 volt D size batteries
  5. Sand paper for removing the insulation from the ends of magnet wire.
    The insulation of magnet wire is like clear paint. Therefore, we use sand paper to remove it. If you are using wires with plastic insulation, you may remove the insulation using pliers.

Results of the Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Once you’re done graphing you should analyze your results and write your conclusion. What is the shape of your graph? Try to make a mathematic equation to project further changes. Revisit the hypothesis you have made at the beginning and check to see if your observations support or oppose your hypothesis. Make sure you discuss what you have discovered.


No calculation is required for this project.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during the experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.